In the process of producing a semiconductor device such as IC and LSI, microfabrication by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X-ray or EUV light is proceeding.
The lithography using electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique, and a high-sensitivity and high-resolution resist is being demanded. Also, in the so-called nanoimprint process aiming at formation of a pattern with a line width of 22 nm or less, it is expected to apply electron beam lithography for the preparation of a fine mold. In particular, the elevation of sensitivity for shortening the processing time is very important but in the positive resist for electron beam or EUV, when elevation of sensitivity is sought for, not only reduction of resolution but also worsening of line edge roughness (LER) are brought about, and development of a resist satisfying these properties at the same time is strongly demanded. The high sensitivity is in a trade-off relationship with high resolution and good LER, and it is very important how satisfy all of these properties.
Also in the lithography using ArF or KrF excimer laser light, it is similarly an important task to satisfy high sensitivity, high resolution and good LER at the same time.
Furthermore, in the process typified by a metal process, the sensitivity, resolution, focus latitude (DOF) performance, LER, skirt trailing and pattern surface roughness are the issues of concern. In particular, LER and pattern surface roughness are in a trade-off relationship with resolution, and mere enhancement of diffusibility of the acid generated incurs decrease of the resolution. It is very important how satisfy all of these properties.
As for the resist suitable for such a lithography process using KrF excimer laser light, electron beam or EUV light, a chemical amplification resist utilizing an acid catalytic reaction is mainly used from the standpoint of elevating the sensitivity. In the case of a positive resist, as described, for example, in JP-A-2000-181065 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”, a chemical amplification resist composition mainly composed of an acid generator and a phenolic polymer having a property of being insoluble or sparingly soluble in an aqueous alkali solution but becoming soluble in an aqueous alkali solution by the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”), is being effectively used.
Various positive resist compositions containing a resin protected by an acid-decomposable group have been heretofore known. For example, European Patent 0919867 discloses a resist composition using a polyhydroxystyrene resin protected by an acetal group, JP-A-2000-284482 discloses a resist composition using a polystyrene resin protected by two different kinds of acid-decomposable groups, and Japanese Patent 3544217 discloses a resist composition using, as the resist solvent, ethyl lactate, propylene glycol alkyl ether and/or propylene glycol alkyl ether acetate.
However, at present, in all of these attempts for improvement, high sensitivity, high resolution, wide focus latitude (DOF) performance, improvement of LER, reduction of skirt trailing, and reduction of pattern surface roughness cannot be satisfied at the same time.